Electric alarm clock



Dec. 25, 1945. vv J. s. RUSSELL ELEC'ITRIC ALARM CLOCK Filed Jan. 2, 1945.

INUENTOR Patented Dec. 25, 1945 ELECTRIC ALARM CLOCK Victor James Samuel Russell, London, England,

assignor to S. Smith & Sons (England), Limited, London, England, a: company of Great Britain Application January 2, 1945, SerialNo. 571,036 In Great Britain October-15, 1943 8 Claims.

This invention relates to electric alarm clocks in which an electromagnetically operated alarm device, such as a buzzer, has its energising coil connected in series with the electric motor which drives the clock movement. In such clocks it is desirable to maintain the electric current within certain limits, particularly if a self-starting motor is used; if the current is too high it is wasteful and may cause noise and if it is too low the motor may fail to start. The object of the present invention is to make provision for adjustment of the current.

According to the present invention, adjustable means are provided for varying the inductance of the energising coil of the electromagnetic alarm device. Preferably, these means comprise an adjustable shunt for the magnetic flux enerated in the said electromagnetic alarm device. In one such arrangement, an electromagnet may have its pole ends arranged side by side and a magnetic element is mounted on one pole and so as to be adjustable towards or away from the other pole end. For example, the adjustable magnetic element may comprise a screw of magnetic material mounted in a threaded hole in one pole and so as to be movable substantially parallel to the pole faces. The screw may be arranged to secure the electromagnet to a support.

In one construction of an electric alarm clock in accordance with the invention, the electromagnetic alarm device comprises a buzzer having a vibrating armature arranged opposite said pole ends and an energising coil encircling said electromagnet, and a self-starting synchronou electrio motor connected in series with said energising coil.

The following is a description of one form of electromagnetically operated alarm device for an electric clock, reference being made to the accompanying drawing, in which:

Figure l is an elevation of the electromagnetic buzzer, and

Figure 2 is a circuitdiagram.

The electromagnetic buzzer shown in Figure 1 comprises a U-shaped core in, one of the limbs l l of which is encircled by an energising coil l 2, and the other of which limbs I3 is secured to a supporting plate [4 by screws [5 and it which engage threaded holes therein.

A vibrating armature H is arranged opposite the pole ends l8 and IS. The screw it in pole end I9 is formed from magnetic material and extends into the gap between the two pole ends and thus provides a shunt for the magnetic flux. The

energising coil I2 is connected in series with a 55 self-starting synchronous motor 20 across an alternating supply 2|, which motor is arranged to drive the clock movement. By adjusting the closeness of approach of the screw it to the pole end IS the inductance of the energising coil l2 may be varied and thus the required strength of electric current passing through the motor and coil may be obtained. The screw I6 may be maintained in the adjusted position by a lock-nut 22 and washer 23.

I claim:

1. An alternating current electric alarm clock comprising an electromagnetic alarm device having an energizing coil, an electric motor connected in series with the energizing coil and ar' ranged to drive the clock mechanism and means for varying the inductance of the energising coil.

2. An alternating current electric alarm clock comprising an electric motor arranged to drive the clock mechanism, an electromagnetic alarm device having an energising coil in series with the electric motor and having a magnetic core energised by said coil so as to provide a magnetic field between two poles thereof and an adjustable shunt for the magnetic flux between said poles.

3. An alternating current electric alarm clock comprising an electric motor arranged to drive the clock mechanism, an electromagnet having an energising coil in series with said motor and having its core shaped to provide two pole ends arranged side by side adjacent one another, a magnetic element movably mounted on one pole end and adjusting means adapted to move the magnetic element towards or away from the other pole end, and a vibratory armature opposite said pole ends.

4. An alternating current electric alarm clock comprising an electric motor arranged to drive the clock mechanism, an electromagnet having an energising coil in series with said motor and having its core shaped to provide two pole ends arranged side by side adjacent one another, a screw of magnetic material mounted in a threaded hole in one pole end so as to be movable towards the other pole end in a direction substantially parallel to the pole faces and a vibratory armature opposite said pole ends.

5. An alternating current electric alarm clock comprising an electric motor arranged to drive the clock mechanism, an electromagnet having an energising coil in series with said motor and having its core shaped to providetwo pole ends arranged side by side adjacent one another, a support for said electromagnet, a screw of magnetic material arranged to clamp the electromagnet to the support and to engage a threaded hole in one pole end and so as to be movable towards the other pole end in a direction substantially parallel to the pole faces and a vibratory armature opposite said pole ends.

6. An alternating current electric alarm clock comprising a self-starting synchronous electric motor arranged to drive the clock mechanism, an electric buzzer comprising an electromagnet which includes an energising coil and which has a vibratory armature arranged opposite its poles, said coil being connected in series with the sy chronous electric motor, and means for varying the inductance of the energising coil.

7. An alternating current electric alarm clock comprising a self-starting synchronous electric motor arranged to drive the clock mechanism, an electric buzzer having a U-shaped core and an energising coil on one limb of the core, said coil being connected in series with the electric motor, a magnetic element movably mounted on the other limb of the core and adjustable towards and away from the first said limb.

8. An alternating current electric alarm clock comprising a self-starting synchronous electric motor arranged to drive the clock mechanism, an electric buzzer having a U-shaped core and an energising coil on one limb of the core con.- nected in series with the electric motor, the other limb being provided with a screw threaded hole, a screw of magnetic material mounted in said holeso as to be movable towards and away from the first said limb, and a support for the buzzer engageable by said screw.

VICTOR JAMES SAMUEL RUSSELL. 

